A touch pad is a data input apparatus widely used instead of a mouse. The touch pad includes touch points arranged in a matrix form on a plane to detect where a user touches it and which direction the point contact moves. Conventionally, a variety of touch pads have been employed. For example, a touch pad may include electrical switches, capacitor-type sensors, resistor-type, or transistor-type sensors, arranged in a plane.
Among conventional touch pads, a touch pad using capacitor-type sensors is commonly used to control the motion of a cursor in notebook computers. The surface of the touch pad using the capacitor-type sensors is covered with an insulating layer, and horizontal lines and vertical lines are arranged at regular intervals under the insulating layer. Capacitors are disposed as electrical equivalent circuits between the horizontal lines and the vertical lines. The horizontal lines constitute first electrodes, while the vertical lines constitute second electrodes.
When a finger, serving as a conductor, comes into contact with the surface of the touch pad, the capacitance between horizontal and vertical lines corresponding to the point of contact differs from that between other lines so that the point of contact can be detected by applying a voltage signal to the horizontal lines and reading variation in capacitance from the vertical lines.
FIG. 1 is a circuit diagram of a conventional electrical touch sensor system. Referring to FIG. 1, the conventional electrical touch sensor system includes a plurality of touch pads 10-1 to 10-N, a semiconductor device 20, and a host computer 30, and the semiconductor device 20 includes a plurality of input/output terminals and a plurality of sense signal generators 20-1 to 20-N. The input/output terminals of the semiconductor device 20 are externally connected to a power supply voltage, a ground voltage, and the touch pads 10-1 to 10-N, respectively. Also, the sense signal generators 20-1 to 20-N of the semiconductor device 20 internally have input terminals connected respectively to the touch pads 10-1 to 10-N via the input/output terminals of the semiconductor device 20, and output terminals connected to the host computer 30 via the input/output terminals of the semiconductor device 20.
The touch pads 10-1 to 10-N generate touch signals indicating a change in electrical state when a touch object such as a finger, which can be regarded as a resistive mean with a certain degree of conductivity, is brought into contact with the touch pads 10-1 to 10-N.
The input/output terminals of the semiconductor device 20 are connected to the power supply voltage, the ground voltage, and the touch pads 10-1 to 10-N, respectively, to form a plurality of channels, so that the semiconductor device 20 can appropriately control touch information generated by the touch pads 10-1 to 10-N and a system requiring the touch information.
In this case, parasitic capacitance is inevitably generated among a plurality of adjacent channels. Thus, an interference signal may be generated between adjacent channels and a difference in touch sensitivity may result between channels. Consequently, respective touch sensor systems have different sizes of touch pads and semiconductor devices and different electrical characteristics. Therefore, the construction of each touch sensor system has conventionally involved an additional tuning process to adjust the sensitivities of respective channels and make the characteristics of the channels uniform.
FIG. 2 is a block diagram of the touch pad and an electrical touch sensor controller of the electrical touch sensor system shown in FIG. 1. Referring to FIG. 2, the electrical touch sensor controller includes a reference signal generation unit 21, a first signal generation unit 23, a second signal generation unit 22, and a sense signal generation unit 24.
Functions of the respective blocks will now be described.
The reference signal generation unit 21 generates a clock signal as a reference signal ref_sig and applies the clock signal to a first signal generation unit 23 and a second signal generation unit 22.
The first signal generation unit 23 always delays the reference signal ref_sig by a first time irrespective of whether a touch object contacts the electrical touch sensor system and generates a first signal sig1.
The second signal generation unit 22 includes the touch pad 10-N with which the touch object is in contact. Thus, the second signal generation unit 22 delays the reference signal ref_sig by a shorter time of the first time when the touch object is out of contact with the touch pad 10-N, and delays the reference signal ref_sig by a longer time than the first time and generates a second signal sig2 when the touch object is in contact with the touch pad 10-N.
In other words, the second signal generation unit 22 generates the second signal sig2 having a phase that leads that of the first signal sig1 when the touch object is out of contact with the touch pad 10-N, and generates the second signal sig2 having a phase that lags that of the first signal sig1 when the touch object is in contact with the touch pad 10-N.
In this case, the touch object may be any object having a predetermined capacitance, for example, the human body in which a large amount of charge can be accumulated.
The sense signal generation unit 30 is synchronized with the first signal sig1, samples and latches the second signal sig2, and generates a sense signal con_sig.
In this case, when the touch sensor system is disposed at a distance from a plurality of touch pads 10-1 to 10-N and a plurality of channels are formed between the touch sensor system and the touch pads 10-1 to 10-N, it is very difficult to make sensitivities of the respective channels uniform.